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-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (http://xlforum.net/forums/showthread.php?t=2073932)

dieselvette 2nd August 2019 20:34

Quote:

Originally Posted by 60Gunner (Post 5767208)
You might be getting crankcase pressure/oil past you guides too.

On 2nd thought, what carb are you running? And aren't you venting to the AC?

I think he is venting to AC - and thats why I think the test with/without AC is telling - In normal setup the small amount of gas out the breathers into the carb is enough to affect the tuning, and then pull the oil cap and the crappy air comes out the oil tank, instead of the breathers? So Hippy says without the AC then the oil cap has no effect, just thinking that confirms my suspicion, but I could be missing something.

Hippysmack 2nd August 2019 22:58

I had my pipes off recently, valves looked fine.
Gotta start writing dates down...
No oil buildup or residue, just light carbon.
I do not have valve guide / seal problems.
I'm not using oil.
Bike runs great, no wet sumping, no oil puking.
Undoubtedly, I'm not having excess CC pressure buildup either.
I thought I'd already established that.

edit: I'm just seeing how it ticks. :)

I'm running a CV and currently venting to A/C.
I recently pulled the carb to adjust the float.
I just pulled it again today (dated now ;)) and blew out everything.
No passages blocked.

I noticed this morning while partially blocking the breather vents with my fingers,
At idle, the vents are puffing outward.
On throttle, they do not and seem to pull a slight vacuum.

dieselvette 2nd August 2019 23:50

Quote:

Originally Posted by Hippysmack (Post 5767245)
I noticed this morning while partially blocking the breather vents with my fingers,
At idle, the vents are puffing outward.
On throttle, they do not and seem to pull a slight vacuum.

What I'm getting at here is why the bike stumbles upon oil cap removal, but with the AC removed it does not. (Or did I misunderstand earlier?)

Any gasses that would normally go in the intake, your bike is tuned to accept and run great in spite of those gasses (no matter how minimal). But when you remove the oil cap, the gasses take a different path (out the tank).

So temporarily venting the gasses from the breathers to atmosphere (by removing the AC) is that why you get different results with the oil cap test?

As a side note, I'm really surprised it makes such a difference, and so the questions earlier about engine condition.

Hippysmack 3rd August 2019 00:58

That's correct.
Oil cap off, A/C off, no stumble.

I put the oil cap back on with the A/C off, engine running.
Then installed the A/C.
The RPM didn't change while doing this (going from not sucking CC pressure to sucking CC pressure).
No harmonic change either.
So I wouldn't think the tuning changed much if any.

60Gunner 3rd August 2019 03:01

Well everything I've read says the the extra unmetered air but that's on cars.
Maybe your breathing is to restricted going into the carb and isnt getting rid of the excess crankcase pressure intoduced thru the vent line from the tank to the cam chest.
Either that or I was thinking something along the lines of the vacuum operated slide being affected.
Venting to atmosphere it doesn't happen.

xlerate 3rd August 2019 03:09

I, too, like the idea of having the crankcase breather coming out of the cam cover as 60gunner and others have done. I'm thinking of something like this, https://www.metcomotorsports.com/pro...p?prod=MBR0009 , at the 12 o'clock position with the idea the oil drains back into the cam cover.

Hippysmack 3rd August 2019 04:28

Two things and I don't think they relate.

First, with the CC pressure puffing at idle and not puffing with throttle,
Running down the road, I'm not pumping into the A/C.
I basically recreated the balloon in my head as I tested with my fingers.
How can it run right if CC pressure is part of the metering (when not pumping into it on a ride)?
I got throttle I ain't used yet... well a little...
105 with some left so far, no sumping, no puking.... no cops. :D

Second, it was quick to froth with the oil cap off at idle (but not with throttle).
Froth is aeration.
There was a ton of time for the sump to empty after startup.
I don't think tuning changed my CC pressure.
I did use some on/off throttle that may not have helped.
Drain hole in the breather cavity not filtering oil that isn't traveling there but the toward the oil cap thus pulling in more air?

I'm having a hard time with the A/C being off in the picture. :doh

edit:
I did check the slide circuit and all seems good.
The carb pulls it's air thru the filter which is way more than what the breathers can deliver... and only at idle, or high revs.

dieselvette 3rd August 2019 04:34

Quote:

Originally Posted by 60Gunner (Post 5767298)
Well everything I've read says the the extra unmetered air but that's on cars.
Maybe your breathing is to restricted going into the carb and isnt getting rid of the excess crankcase pressure intoduced thru the vent line from the tank to the cam chest.
Either that or I was thinking something along the lines of the vacuum operated slide being affected.
Venting to atmosphere it doesn't happen.

You're thinking of manifold pressure, but that's behind the carb.

When I say "tuning" I guess is confusing. It's not about pressure or flow from the breathers, but the fact that it's hot air with no oxygen, and possibly oil vapors. That results in a different mixture than with 100% fresh air. At idle this makes up a percentage of the total intake air. But, if the bike is tuned to idle on this shi++y air then OK you don't know the difference until the vents are moved (or oil cap removed).

The more you open the throttle, the less impact this stale air will have on your mixture as it becomes a smaller % of total air. (But, it still has an impact on performance).

Hippysmack 3rd August 2019 04:44

Quote:

Originally Posted by xlerate (Post 5767300)
I, too, like the idea of having the crankcase breather coming out of the cam cover as 60gunner and others have done. I'm thinking of something like this, https://www.metcomotorsports.com/pro...p?prod=MBR0009 , at the 12 o'clock position with the idea the oil drains back into the cam cover.

PCVs made for autos seems to be frowned on although many are apparently using them.
The check valve should be in the bottom on that one.
For $60 hope it works (may be a spring / check ball they don't say).
I'd like to see a reed valve on a cam chest mod.

Post the results and pics when you've got it done. :)

dieselvette 3rd August 2019 04:48

Quote:

Originally Posted by Hippysmack (Post 5767190)
the oil cap off is allowing CC pressure to escape and atmosphere to enter the engine.

Not entirely. The CC vent to tank is 1/4" hose and what 2ft long? The air doesn't just turn around and flow backwards that easily. Which is why having say, an open-ended 6ft length of hose would be as good as any umbrella valve in many scenarios.

Think of a tuned exhaust and cam overlap - exhaust valve is still open after exhaust stroke, while piston is on the way down, yet the air continues to flow out the exhaust valve because of velocity. By the time air starts to slow down the next pressure wave is there to keep it moving.


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